Shock strut



Aug. 1, 1939. c. v. .JOHNSON SHOCK sTRUT Filed Deo. .'50, 1936 3 Shaets-Sheet 1 INVEN'I'UR. gm V///Msm/ ATTURNEY.

All@ L l939- c. v. JOHNSON i 2,167,928

SHOCK STRUT A TTORNEY l Aug, l, 1939.

c. v. JOHNSON TORNEY watchin-ld l,

nitraat snaps s'rnpr Fari t7'. dohn'son, Fourth hond, llnd., assigner to hendiu Froducis Forporation, South hand, ind., a corporation et indiana Application hecember td, ibid, denial hln lillhtbt arated by yielding means associated with one oi them. i

yit has been ioundthat when the load is suddenly released from the strut, the' chambers sepait rate too rapidly, thereby subjecting the retaining means holding the strut members from separating to rather severe impact loads. This tendency or the strut to move to the extended position too rapidly has in the past been overcome by 2@ positioning a check tube around the metering pin. The check tube incorporated a check valve to permit the liquid to now freely through the orince separating the chambers when the strut was subjected to load. When the load was removed trom M the strut and 4it was moving toward the extended position, the ilow oi liquid to the orihce between th'` chambers was restricted. 'llhe rapidity with ,which the strut could move to the eirtended position was thus controlled'.

llt has also been found that the metering pins oi shoclr absorbing struts, which have relatively long taper pins with large clearance in the orince are, under certain operating conditions, subject to vibration which cause thev metering pin to 35 hammer the member forming the orifice, enlarging .it and varying the flow characteristics oi the liquid from one chamber to the other.

An object of this invention is therefore to provide means to delay the separation oi the tele- 40 scoping members of a shock absorbing strut.

A further object is to utilize the space between the movable elements of a shock strut to trap liquid to controlI the rapidity oi the separating movement of the strut.

45 Another object is to provide a reservoir to re- Y ceive liquid, through 'a check valve, when the strut is compressed, and a metering orifice controlling the rate of liquid flow from the reservoir to control the rate of extension of the shock strut. m A still further object of the invention is to provide a concentrically disposed expansible liquid chamber between the telescoping cylinders of a shock strut wherein means are provided to vary the rate of liquid ow toand from the concentric 55 chamber byapressureactuated valve to control lei. arrop the rate oi relevant movement between the cylinders.

ii'et a iurtherobject oi .the invention is to provide a constant diameter metering pin having spaced grooves in itsside walls adapted to project through a lined oriiice to control the rate or liuuid flow through the orifice.

Another object is to forni a constant diameter, limited vibration, metering pin having a plurality oi spaced grooves oi variable depth adapted to w project through a hired orirlce to control the rate ci liquid flow through the orifice and to equalize liuuid pressure around the metering pin.

@ther objects and advantages of this invention will be apparent from the following detailed deld scription thereof, considered in connection with the accompanying drawings, submitted for purposes oi illustration only, and not intended to deune the scope of the invention, reference being had lor that purpose to the subjoined claims.

In the drawings, wherein similar reference characters reier to similar parts throughout the several views: l

Figure l is a view showing a shock absorbing r strut embodied in an airplane; 2d

Figure 2 is a side elevation, partly in section, .oi a shoclr strut embodying thel present inven- 'ion;

Figure d is an enlarged sectional view of a portion of Figure 2;

- Figure d is a view similar to Figure 3 showing a modified iorm oi" the invention;

Figure 5 is a view similar to Figure 3 showing a further modined form of the invention;

Figure 6 is'lgen'erally similar to Figure 3 and 35 shows another embodiment of the invention;

Figure 7 is alsoa view similar to Figure 3, and shows a still further modified form of the invention.;

Figure d is a vertical section through the 40 metering pin and orifice assembly of this invention;

Figure 9 is a view taken substantially on the line b-b or Figure 8;

Figure 10 is a view similar to Figure 9 showing 45 a modified form of the invention; and

Figure lll is also a view similar to Figure 9, showing a still further modified form of the invention. 50

Referring more particularly to Figures'l to 3 there is shown for purposes of illustrating this invention, a shock absorbing strut I0 interposed between a portion of a fuselage I2 of an airplane,

and a landing wheel It. j One or more auxiliary 55 y' support members I6 may be employed to securely connect the wheel |4 to the fuselage I2.

As will be observed, the shock strut I8 is mounted in the' substantially vertical position. It comprises an upper or uid cylinder I8 connected to the fuselage I2, adapted to slide into a liquid cylinder 28 connected to the member supporting the wheel I4.

Referring more particularly to Figures 2 and 3 it will be observed that a metering pin 22 fixed in the cylinder 28' projects through an orifice 24 formed in a member 26 closing the lower end of the cylinder I8. The cylinder 28 is normally filled with a liquid, and the cylinder I8 :is nor- =mally filled with a liquid and a compressible fluid such for example as air. When the strut I8 is subjected to load, liquid flows from the "cylinder 28 through the orifice 24 past the metering pin 22, into the cylinder IB. The force of the load to which the strut is subjected is absorbed and either dissipated or stored by forcing the liquid to fiow through the orifice and by compressingr the fluid in the chamber I8. The cylinders I8 and 218 are guided and kept in proper telescoping relation by rings 28 and il@ threaded on the ends of the cylinders i8 and ZEE respectively as shown. A ring 32 carried by a shoulder 34 formed in the cylinder 28 cooperates with the rings 38 and 36 to compress packing rings 38 therebetween to prevent leakage of' liquid from the strut.

A concentric chamber 48 is formed between the cylinders I8 and 28 and the relatively movable rings 28 and`32. The chamber 48 communicates with the interior of the,cylinder I8 by means oi' horizontally and vertically disposed ports 42 and 44,. These ports may be of any desired size and number to admit liquid to the. chamber 48 when the cylinder I8 slides into the cylinder '28". The ports 44 may be controlled by a pressure actuated check valve 48 movable between a stop member 48 threaded onto the cylinder I8 and the upper surface of the ring 28. Metering orices 58, ex-

-tending through -the walls of the cylinder I8 communicate with the chamber 48.

The operation of this device is as follows. When the strut I8 is subjected to load, the cylinder I8 is forced downwardly into the cylinder 28, whereupon liquid from the cylinder 2|8 is forced through the orifice 24, past the metering pin 22 into the cylinder I8. As the cylinders move relative to each other the volume of the concentric chamber 48 increases, whereupon suction is created therein to draw liquid through the ports 42, 44 and 58, past the check valve 48 into 'the chamber 48. When the telescoping action ceases the pressure of the compressed fluid in the cylinder I8 urges the cylinders I8 and 28 apart. When the cylinders begin to separate pressure is exerted in the chamber 48, whereupon the check valve 46 is forced to its seat to close the ports 44. The liquid in the chamber 48 is then forced through the metering ports 58 into the cylinder I8. The size and number of the metering orificesv 58 may of course be varied to control the rate of separating movement of the cylinders I8 and 28' as desired. As the strut approaches the fully extended position, the orifices 58 pass under the ring 32 thereby reducing the rate of flow of liquid from the progressively decreasing chamber 48 to an amount determined by clearances around the piston and the piston tube. When the strut reaches the fully extended position, the stop member 48 engages the ring 32 to prevent separation of the cylinders.

the addition of |818 in each of these flgures'hav- 5 ing therefore been applied to corresponding parts. In the embodiment illustrated in Figure 4, the ports |42 extending through the walls of the cylinder II8 communicate with the concentric chamber |48. AThe upper end ofthe ring |28 is 10 shaped to form a shoulder |52 proportioned to be engaged by the outer edge of a ring |58. The ring |54 is slidably mounted on the cylinder Ii, and in its extreme upward position engages a stop member or ring |55. forms a check valve which moves away from the shoulder |52 of the ring |28 to permit communication between the inside of the cylinder ii8-and the chamber S88 when the cylinders Ili and |28 are moving in the 'telewoping direction. When 20 rthe cylinders IIB and t28 separate, the volume of chamber M8 decreases whereupon uid pressure is developed in the chamber which cooperates with the force of gravity to urge the ring i5@ downwardly to close the ports M2. liquid rin the chamber M8 is then metered through the orifices |58 to control the rate of 'the extending movement of the, strut. The ring |32 is formed with a notch I 58 to receive the stop member |56. When the strut reaches the 30 fully extended position the ring |54 contacts the rings |28 and |32 to prevent separation ofthe cylinders II8 and |28. It will also be observed that in this embodiment of the invention, the

oriices |58 are closed by the ring |32 when the 35 strutis in the fully extended position.

In the embodiment illustrated in Figure 5, a ring 288 isl slidably mounted on the cylinder `2|8 between the ring 228. The ring 268 may move between a shoulder or stop 262 formed on 40 the cylinder and the upperend of the ring 228. The ports' 242 communicate with the chamber 248 above the ring 228, and the metering orices 258 communicate with the chamber 248 below the shoulder 262. portioned to close .the ports 242 or the metering orifices 258 whenmoved to one extreme position or the other.

When the strut is subjected to load, and the l cylinder 2I8 slides into the cylinder 228, the 80 chamber 248 is enlarged. Suction is therefore exerted in the chamber 248 to move the ring 288 against the stop 262 and draw liquid into thev chamber 248 through the ports 242.

When the strut i's expanded pressure is exerted 55 in the chamber 248, whereupon the ring 28| is forced downwardly to close the ports 242 andA open the metering orifices 258. The liquid in the chamber 248 is then metered through the orifices 258 to retard the expanding movement of the strut. In the fullyextended position the ring 288 is engaged by both of the rings 228 and 232 to prevent separation of the cylinders. It will be understood that if desired the metering orifice 258 may be positioned above the shoulder 65 262 in such a position as to be closed by the ring 232.

In the embodiment illustrated in Figure 6, the ring 328 is formed with an inner groove, .forming a concentric .space 318 between the upper mi 70 of the ring 328 and the cylinderJIB. A stop, ring 4 312 is ilxed to the cylinders 3,I8 adjacent the upper end of the ring 328. 'Ihe ports 342 project through the walls of the cylinder 3|Iv below the stop ring 312 and communicate. with The ring i5@ thus 15 The 25 The ring 288 is preferably pro- 45 iii the concentric space iid. il checlr valve which may be in the form oi a disc tilt is slidably mounted between the upper end oi the ring dit andthe stop ring dii. The disc till operates to open counication between the ports iii and the chamber 34d when the strut is collapsing and the chamber 34d is therefore increasing in vol and to close communication between the chamber ,dit and the ports iti when the strut is sanding and the chamber itil is subjected to pressure. When the strut is expanding the litiuid in the chamber itil is oi course metered through the metering'orinces itil m control the rate oi expansion oi the strut.

in the iully extended position the metering orii'lces are closed by the ring and the stop ring dit engages the ring to prevent separation oi the cylinders iilli and ddii.

iillgure i shows a further modiiied iorm oi the `invention wherein the ring dit, which clamps the orince carrying member to the endl oi dit the cylinder dit is provided with an upstanding ring itil to engage the ring dit) to prevent separation oi the cylinders dit and ddii.

in this embodiment it will be observed that a pressure actuated valve member dit moves between a stop ring ddii hxed to the cylinder did, and a shoulder litt formed on the ring dit. 'lihe `valve member tti operates to close or open com ysa liti

dii

iid

munlcation between the chamber ddii and the ports lidi in the walls oi the cylinder lill depending on whether the chamber ddii is subjected to pressure or suction as the strut is compressed or expanded. ln thisembodiment the meterina oriiices ddii are closed by the ring ddii when the strut is in the extended position. A

lugares t and il show the metering pin and associated parts in detail. lt will be observed that the pin ii is iixed in the lower end oi the cylinder iii and projects through the oriiice iid liormed in the member iiil clamped to the lower end oi the cylinder iii by the ring as more clearly shown in Figure d.

The pin it is oi" constant diameter throughout its length; has relatively small clearance with the walls iorming the oriilce dd, and is ici-med with grooves id on opposite sides thereoi. m will be observed in Figure d, the depth oi the grooves it vary over the length ci the pin to progressively vary the edective area oi' the oridce iii as the metering pin it is projected therethrough. in the illustrated embodiment,the eliective area oi the orince iii is relatively small during the initial stages oi operation when the cylinder it begins to slide into the cylinder iii, as represented by the section d oi the pin. in the section b oi the pin the grooves iii are progressively deeper; thereby progressively increasing the effective orice area. in the section il' the grooves are 0i constant depth and in the section D the groovesr are progressively more shallow. These relations may oi course be varied to 'accomplish any desired results in a particular installation.

.attention is directed to the iact that ii the pin iii starts to vibrate, the relatively small clearance between the pin and the walls `forming the oriiice, limit the oscillations oi the pin to prevent the building up of suilicient force in the pin to ay balanced structure which will tend to retard surging oi the liquid, and will limit vibration oi the pin it, The pin 22 being oi constant diamecenter oi the pin. d more rigid pin which is less susceptible to vibration is thereiore produc lllianuiacturing tolerances thereiore need not be maintained between such close limits, whereupon the manuiacturing costs may be decreased.

iii' desired the pin di may have grooves it oi constant depth as illustrated in litigare ld. in this embodimentthe eiiective area oi the oridce iid may be varied by expanding the grooves laterally oi the pin as shown.

ltiaure ll shows another desirable embodiment wherein the pin is iormed with spaced nrooyes 'il oi' varying depth and width to enge the eiiective area ci the oriiice dd.

Illihe embodiments illustrated in meines id and li sive a large solid section at the central portion oi the pin which is desirable because the pin is less apt to iail became ci fracture or impact loads to which it might be subfiected when not having the orifice itl therein, may be termed with smooth curved walls, instead of the dat upper surface, to iorm a streamlined structure to guide the huid ilowing from the cylinder iii to the cylinder iii, thereby decreasing turbulence oi the duid.

lit is understood, oi course, that the' strut shown in the various embodiments hereoi may be inverted, the outer cylinder being positioned above the inner cylinder iii. ln this case the linuid would oi' course till the lower cylinder, which in the inserted position would be the inner cylinder iii..

twiile the invention has been described with particular reierence to several desirable embodi-l ments, it is to be understood that the disclosure is illustrative only, and that various features may be combined in anyidesired manner, and that many changes can be made without departm iii dit

dit)

dit

ing trom the spirit oi the invention as deiined by titi means to admit liquid to said chamber ireely the cylinders are moved in the telescopingdirection and to close the chamber to huid when the cylinders are moving in the extended direction,

and metering oriiices to permit .escape oi linnid from said chamber.

2. lin alnfdro-pneumatic shoclr strut, a pair ci telescoping cylinderaliduid and iiuid in said cylinders, means including a metering pin and an orliice carrying member inter-connecting the cylidd inders to control the ilow oi liuuid irom one cylinder to the other, a chamber between the cylin-y ders and communicatingwith one oi said cylin-a ders to receive liquid thereirom when the cylinders are moving in the collapsing direction,- pre.,- sure responsive means controlling the admission oi liquid to said chamber, and orihce means to permit the escape oi liquid from said chamber as the cylinders are moving in the extended direction.

3. lin a shoclr strut an outer liquid cylinder, an

inner duid cylinder, means including a member having an orifice therein closing the fluidfcylinder and communicatingwith the liquid cylinder, and a metering pin carried by the liquid cylinder and projecting through said orifice to vary the effective area of the orifice as the strut is progressively compressed, said metering pin being formed with spaced grooves extending longitudinally thereof and proportioned to vary the effective orifice area as the fluid and liquid cylinders move in the telescoping direction to interpose a high constant resistance followed by a\decreasing resistance followed by a constant resistance followed by-an" increasing resistance.

4. A shock strut comprising a liquid cylinder, a fluid cylinder, means including a member havin'g a fixed orifice therein positioned between the cylinders, means including-a metering pin 'associated with one of said cylinders and projecting through said orifice to vary the effective'area of.

the orifice esthe cylinders move with reference to eachother, means to control the movement of the strut comprising a longitudinally expansible tive area of the orifice as the chamber positioned between the cylinders adapt- -ed to freely receive liquid through main and auxiliary orifices as the strut is compressed; means to close the main orifices' when the strut moves in the expanding direction, and means to. close the auxiliary orifices. when thestrut approaches the fully extended position.

5. In a shock strut an outer liquid cylinder, an

inner fluid cylinder, means including a member having an orifice therein closing the fluid cylinder and communicating with the liquid cylinder, a metering pin carried by the liquid cylinder and projecting through s-iid orifice to vary the effecstrut is progressively compressed, saidjmetering pin being formed with spaced grooves extending longitudinally thereof and proportioned to vary the effective orifice area as the fluid and liquid cylinders ,move,

6. In' a shock strut, a' pair of telescoping cylin- 4,

ders, liquid and fluid in the cylinders, means including a plurality of ringsfcarried by the cylin-- ders to maintain the strut in assembled relation,

a liquid-chamber between the cylinders, spaced upper and lower connecting means between one of the cylinders and said chamber, and pressure responsive valve means to close the lowernconnecting means when the `cylinders are moved in the extending direction. i

'7. In a shock strut, a pair of telescoping cylindersjliquid and -compressible fluid in the cylinders, a liquid chamber between -the cylinders, main and auxiliary orifice means extending through the walls of one of the cylinders to interconnect one of said cylinders and said chamber, and pressure responsive valve means controlling the main orifice to open the orifice when the cyl-l inders are moving in the telescoping direction and to close said orifice when ,the cylinders are moving in the extending direction. f

8. In a shock strut, inner and opter telescoping cylinders, liquid and compressible uid in the cyltion,

when the strut approaches the fully extended means, a liquid ch inders, spaced stop means carried by the outer cylinder, sealing means positioned between said stop means, a liquid chamber between the cylinders and interposed between said stop means, main and auxiliar.;r connecting means between one of the cylinders and said chamber, and check valve means concentrically mounted with refer- Aence to one of the cylinders to close the main connecting means 'when the cylinders are moving in the extending direction.

9. In a shock strut, a pair of telescoping cylinders, liquid and fluld'in the cylinders, means including a plurality of rings carried by the cylinders to maintain the strut in assembled relation,

a uid chamber between-the cylinders, spaced upper and lower connecting means between one of the cylinders and said chamber, andA pressure responsive valve means to close the lower conlne'oting means when the cylinders are moved in the extendingl direction, the upper connecting means being closed by one of said rings as the vcylinders `approach the fully extended position.

10. In a shock strut,'i1ner and outer telescoping cylinders-liquid and compressible fluid in the cylinders, al liquid chamber between the cylinders, vertically spaced main and auxiliary orifice means interconnecting the inner cylinder and said chamber, and pressure responsive valve means concentricallymounted on the inner cylinder controlling the main orifice to open the orifice when the cylinders are moving'in the telescoping direction and to close said orifice when f in theextending direc-y the cylinders are moving the auxiliary orifices and means .to close position.

'11. In'a shock strut, inner and outer telescopy ing cylinders, liquid and fluid in the cylinders,

spaced stop meanscarried by the outercylinder; sealing means positioned between 'said stop ber between the cylinders, main andA auxiliary connecting means between one o f the cylinders and said chamber, and check valve means concentrically mounted with reference to one of the* cylinders to close the main connecting neans when. the

in the extending direction, the auxiliary con- '.necting meansbeing closed by said stop means as the strut approaches the fully extended position. v

12. In a shock strut,'inner and outer telescoping cylinders, vliquid and fluid in the cylinders, means including rings outer cylinders to maintain the strut in assembled relation, a duid chamber betwen' the cylinders,

spaced upper and lower connecting means between the inner cylinder and said chamber, and

pressure responsive valve means concentrically mountedv on the inner cylinderjadjacent said-ring to close the lower connecting'means whe the cylinders are moved in the extending directi 13. In a shock strut, inner and outer telescopcylinders, spaced stop means carried iby the outer cylinder, sealing means positioned between said stop means, an abutment` 4carried by the inner cylinder and adapted to engage said stop means,

a liquid chamber between-the cylinders, main and auxiliary connecting means b etween one of the cylinders and'sald chamber, and check valve means concentrically lmounted with reference to the inner cylinder adjacent said abutment to close the main connecting means whenf the cylinders are moving in the extending direction.

14. A shock strut comprising inner and outer carried4 b y the inner and.

cylinders aremoving l ing cylinders, liquid andmpressible fluid in the menen inders, a liquid, chamber between the cylinders,v

main and auxiliary connecting means between one of the cylinders and reid cliber, cne'clr valve means concentrically mounted with reference to one of the cylinders to close the main connecting means when the cylinders are moving in the extending direction, and means to close the auxiliary connecting means ae the strut ap= nroaches the fully extended position.

i5. In a snoek strut, inner and outer telescopf ing cylinders, liquid and compresslble fluid in the cylinders, e liquid chamber between the 'cylinders main and auxiliary connecting means between one oi' the cylinders and said chamber, and checit valve means concentrically mounted with reference to the inner cylinder .to close the main connecting means when the cylinders are moving in. tlie extending direction.

16. A. metering pin for a hydro-pneumatic shock strut including telescoping liquid and uid cylinders and an orifice-carrying member, com

pricing a longitudinally extending body member adapted to project through the orice-carrymg member and provided with grooves formed in the side wells thereof to cooperate witlg the orice- 'carrying'.ineniberrto viriterpoee a. constant high resistance to the initialshock followed by a, de-

creasing resistance ,followed Vby a constant re slstance followed by an increasing resistance..

'CARL v. JoHNsoN. 

